The object of these studies is to understand how cells regulate mRNA translation during the growth cycle and in response to fluctuations in their environment. We are studying the mechanism of the reversible reduction in the rate of polypeptide chain initiation seen in cells in several physiological states. We are also studying the mechanism by which certain mRNAs are preferentially translated in cells in which protein synthesis has been reduced by hyperthermia. Normal and tumor-derived cells will be compared. Using mechanisms previously shown to regulate initiation of protein synthesis in cell-free extracts as a working hypothesis, we are testing whether similar mechanisms operate in living cells. These problems will be analyzed by measuring initiation complex formation in intact cells and cell extracts. We will also measure changes in the extent or rate of phosphorylation of initiation factors in living cells. We will determine the relative concentrations of heat shock mRNAs induced during hyperthermia in HeLa cells by hybridization to cDNA probes. We will assay the relative efficiency of initiation of mRNAs purified from control and hyperthermic cells using cell-free translation systems prepared from control and hyperthermic cells.